Magnetic machines, sometimes called "dynamos," are known for converting mechanical energy into electrical energy, or for the reverse process, converting electrical energy into mechanical energy. In the first case, the magnetic machine is called an "electrical generator." In the second case, the machine develops mechanical power, and is thus called a "motor."
Whether acting as a generator or a motor, magnetic machines function because of a relative motion between electrical conductors on a rotor or armature and a magnetic field. The magnetic field may be stationary and the electric conductors revolve through it, or the electrical conductors may be stationary and the magnetic field structure may revolve. It is also possible for both the conductors and the magnetic field to be in motion in a functioning magnetic machine.
In case of generator function, the relative motion between the electrical conductors and the magnetic field produces an induced electro-motive force, sometimes called an "EMF" or voltage, and an associated current in the active conductors. Generally, the EMF and current that are produced are alternating in direction, and so sometimes a "commutator" is used to make the electric current unidirectional in the external circuit of the magnetic machine. However, there are certain magnetic machines which do not have a commutator and in which the associated currents and voltages are not alternating. These types of magnetic machines are called "homopolar" machines, and are sometimes also called "acyclic dynamos."
In a homopolar machine having coaxial rotor conductors, as well as in other types of magnetic machines, the instantaneous EMF induced in a conductor having a length, L, moving with a velocity, V, within and perpendicular to a magnetic field density, B, is generally given as: EQU E=BLV,
which is the well known Faraday induction law for the relative motion between the electrical conductors and the magnetic flux. See, e.g., R. G. Kloeffler et al., Direct-Current Machinery, Chapter 2, p. 13 (1948), the teachings of which are specifically incorporated herein by reference.
The generalized induction equation in prior homopolar machines is known by those with skill in the art as: ##EQU1## where .phi. is the magnetic flux which can be dependent in time. For homopolar machines having disc rotors and radial conductors, ##EQU2## alone, where.phi.=B.multidot.A, and A is the area of the disc rotor. This is the well known Faraday/Lenz law of induction. Thus for the disc rotor machine, the induced EMF can be written as where r is the length of one rotor radial conductor segment and m is the rotational speed of the disc in turns/second.
Because of the construction of typical homopolar machines, the conductors on the rotor are adapted to always cut magnetic flux in the same direction. Due to this arrangement, the generated EMF and the current flow are steady and in the same direction at all times, which eliminates the need for a commutator and which avoids the difficulties which arise from reactance voltages.
Since the lengths of several individual rotor conductors of a homopolar machine are usually extremely short, only low voltages and high currents can be produced with current homopolar machines. Thus, typical homopolar machines have had voltage ratings of 3 volts at 6000 amps, and 3 volts at 4500 amps, for example.
Thus while the homopolar machine has heretofore been useful in low voltage applications, it has been virtually useless when high voltages are necessary, thereby forcing the electrical engineer to utilize a standard multipolar magnetic machine having a commutator which is expensive and inefficient. Alternatively, electrical engineers have used rotary converters which operate only at low voltages, or solid state converters which are complicated and expensive. These options are therefore generally not realistic for many DC power generation and transmission requirements, and so there does not currently exist a simple magnetic machine to provide a solution for generation of high DC voltage, for straight transformation of DC voltage, and which is operable for a wide variety of voltage applications.